1. Field of the Invention
The present invention relates to a low temperature start of a fuel cell, and more particularly, a fuel cell system for warming up using a hydrogen storage alloy.
2. Description of Relevant Art
Attention in recent years has been focused on a fuel cell electric vehicle (FCEV) from a perspective of suppressing a discharge amount of carbon dioxide that is a cause of global warming. A fuel cell (FC) reacting hydrogen (H2) with oxygen (O2) in air electrochemically to generate electricity is mounted in the fuel cell electric vehicle. Electricity generated by the fuel cell is supplied to a travel motor, and driving force is generated.
Moreover, the temperature where the fuel cell realizes the maximum performance is decided. For example, in a proton exchange membrane (PEM) type fuel cell for which attention has been focused as a power plant of the fuel cell electric vehicle, the temperature is about 80° C., and if the temperature is low, the power generation performance (electromotive force) is reduced. Thereby, when the fuel cell electric vehicle is started in winter or in a cold district, it is necessary to warm up the fuel cell (that is, heat or warm the fuel cell to a prescribed temperature).
Conventionally, the fuel cell has been warmed up by the following methods.
(1) Warm-up due to an electric heater; An electric heater is made to generate heat by a power supply provided in a battery mounted in the fuel cell electric vehicle and in a garage or the like, and the fuel cell is warmed up by the heat (for example, Japanese Unexamined Patent Publication No. H7-94202).
(2) Warm-up due to a hydrogen combustor; Hydrogen, methanol and gasoline or the like mounted in the fuel cell electric vehicle as fuel (raw fuel) are supplied to a catalytic combustor or the like and burned. A fuel cell is warmed up by the combustion heat (for example, Japanese Unexamined Patent Publication No. 2001-118593).
(3) Warm-up due to self-heat generation of a fuel cell; When the power generation of the fuel cell is started, the fuel cell is warmed up by using heat generation (so called self-heat generation) due to the electrochemical reaction of hydrogen and oxygen (for example, Japanese Translation of International Application No. 2000-512068, equivalent to WO97/48142).
(4) Other warm-up; A fuel cell is warmed up by a thermal storage agent or an exothermic agent (for example, Japanese Unexamined Patent Publication No. H10-144333).
On the other hand, the applicant has focused attention on a hydrogen storage alloy that generates heat when the hydrogen storage alloy absorbs hydrogen, and the heat generated in this case can be used for the warm-up of hydrogen consumption apparatuses including the fuel cell, and a hydrogen storage alloy capable of being repeatedly used. The applicant has conventionally proposed a technique that a hydrogen storage alloy tank for warm-up is attached to a fuel cell system and the fuel cell is warmed up by the heat generated by introducing the hydrogen into the hydrogen storage alloy tank (Japanese Unexamined Patent Publication No. 2002-222658).
In this fuel cell system, a primary regulator and a secondary regulator are arranged in order to decompress between a high-pressure hydrogen tank and the fuel cell in two steps. The hydrogen extracted from between the primary regulator and the secondary regulator is introduced into the hydrogen storage alloy tank, and the fuel cell is warmed up by heating a cooling liquid of the fuel cell by the heat discharged from the hydrogen storage alloy. After the warm-up operation, the hydrogen is discharged from the hydrogen storage alloy by heating the hydrogen storage alloy tank using the cooling liquid of the fuel cell heated. Electricity is generated by making the hydrogen attract to the fuel cell from the downstream side of the secondary regulator, and the hydrogen storage alloy arranged in the hydrogen storage alloy tank is simultaneously reproduced.
However, it is not preferable that a battery is consumed in the warm-up due to the electric heater of (1). Electricity may not be sufficiently supplied from the battery at a low temperature. When the power supply is used, the fuel cell cannot be warmed up at a position where power supply is not available such as on a road. It is not preferable that the fuel cell consumes fuel (raw fuel) which should be used for power generation in the warm-up due to the hydrogen combustor of (2) or the like. In the warm-up due to the self-heat generation of the fuel cell of (3), the fuel cell cannot be warmed up in the situation in which the fuel cell cannot generate electricity. It is not preferable that the fuel (raw fuel) is consumed for warm-up. In the case of the thermal storage agent or the exothermic agent of (4), it is difficult to take out heat when required, or it is difficult to use the thermal storage agent and the exothermic agent repeatedly. That is, in the prior art, energy is required only for warm-up, and energy which should be used for power generation is wastefully consumed. Since a dedicated heater and a dedicated hydrogen combustor or the like which can be used only for warm-up, or a dedicated thermal storage agent and a dedicated exothermic agent or the like are used, a problem exists in that the fuel cell system is enlarged. Although it is necessary to warm up quickly, in order to satisfy this demand, further consumption of energy and a large-sized warm-up device are needed. The warm-up must be able to be easily performed by a simple configuration.
On the other hand, since the fuel cell system described in JP unexamined patent publication No.2002-22258 uses the hydrogen used for warm-up as the fuel of the fuel cell after the warm-up operation, the fuel cell system is different from a warm-up method due to the electric heater and the hydrogen combustor or the like, and has no problem with consumption of electric energy and hydrogen fuel. Also, the fuel cell system generates heat very quickly when the hydrogen storage alloy absorbs the hydrogen, and can be promptly warmed up. In addition, the fuel cell system can be warmed up regardless of situations such as outside air temperature in a comparatively small device.
However, since the hydrogen from the hydrogen storage alloy tank is discharged to the downstream side of the secondary regulator while the hydrogen is introduced to the hydrogen storage alloy tank from between the primary regulator and the secondary regulators in the fuel cell system, the following problem has existed. That is, since the number of apparatuses such as a solenoid valve provided in pipes connected to the hydrogen storage alloy tank or in the pipelines thereof is increased, the configuration of the device becomes complicated, and the cost of manufacturing is also increased. Although the supply amount of the hydrogen to the fuel cell is controlled by the adjusting pressure of the secondary regulator, since the hydrogen flows to the downstream side of the secondary regulator from the hydrogen storage alloy tank, it is not avoided that the hydrogen serves as a disturbance and the control becomes complicated, or the power generation state of the fuel cell becomes unstable.
Therefore, there is a desire of a fuel cell system which has a simple configuration and realizes the efficient warm-up of the fuel cell without causing problems described above.